1. Field of the Invention
The present invention relates to a drill guide for accurate tibial tunnel placement both inside and outside the knee in endoscopic ACL reconstruction and, more specifically, to a drill guide with a marking hook which references the posterior cruciate ligament and has a slot at its distal end for facilitating drilling of a guide pin.
2. Description of the Related Art
In the past, the intra-articular entry point of the tibial tunnel has tended to be placed too far anterior, resulting in roof impingement and delayed graft failure. See, e.g., S. Howell, "A Rationale for Predicting ACL Graft Impingement by the Intercondylar Roof, A Magnetic Resonance Imaging Study", Am. Jour. Sports Med., Vol. 19, No. 3, pp. 276 (1991), incorporated herein by reference. This problem has occurred largely due to the absence of any constant, bony landmarks in the intercondylar notch which can be used to orient placement of guide systems for accurate, reproducible, tibial tunnel guide-pin placement.
Also, the tibial tunnel exit point outside the knee has tended to be placed too close to the joint line. This results in a short tibial tunnel such that the tibial bone plug of a completed bone-patellar-tendon-bone autograft reconstruction resides outside the tibial tunnel and interference screw fixation cannot be used. A second problem caused by a high, tibial-tunnel exit point is that the angle of the tibial tunnel with respect to the joint line is too small, which will not allow transtibial tunnel instrumentation to reach the isometric area on the lateral femoral condyle to create a femoral socket for graft fixation.
The one constant anatomic structure in the intercondylar notch of the anterior cruciate ligament (ACL) deficient knee is the posterior cruciate ligament (PCL). See, e.g., C. Morgan et al., "Arthroscopic Meniscus Repair Evaluated by Second Look Arthroscopy," Am. Jour. Sports Med., Vol. 19, No. 6, p. 62 (1991), herein incorporated by reference. In the intact knee, there is an important anatomic interaction between the ACL and the PCL at their midpoints, whereby the intact ACL actually wraps around or bends over the PCL in terminal extension. This dynamic interaction is an integral part of the "screw home" mechanism of the knee. Ideally, during ACL reconstruction, the entry point in the knee for the tibial tunnel should be made far enough posterior to reconstruct this important relationship between the ACL graft and the intact PCL.
The proper entry point for tibial tunnel guide pin placement resides 7 mm anterior to the leading edge of the PCL at the level of the intercondylar floor. A 7 mm diameter graft placed through a 7 mm tibial tunnel centered at this point will: 1) reach an isometric femoral socket directly in line with the tibial tunnel with the knee in 70-80.degree. of flexion; 2) avoid roof impingement in full extension with a minimal notchplasty; and, 3) reconstruct the "screw home" mechanism and the interaction between the ACL graft and the intact PCL.
Previous instruments have been developed for marking the correct location of the tibial tunnel. See, for example, U.S. Pat. No. 5,269,786. Such instruments use marking hooks which have a tip that disadvantageously blocks a surgeon's view through the arthroscope of the drilling site at the end of the tibial tunnel. Without visual verification, it can be difficult for the surgeon to determine when drilling is complete. Due to the lack of a visual cue for completion of the tunnel drilling, surgeons have often relied upon the impact of the drill upon the marking hook as an indication of completion. However, this is undesirable, since such impact can create metal shavings which may harm the joint and are otherwise undesirable. The impact can also cause deflection of the drill, resulting in peripheral tissue damage or inaccurate tunnel formation.